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  • 1
    Electronic Resource
    Electronic Resource
    Long-duration high-energy proton events observed by GOES in October 1989 (1998)
    Springer
    Annales geophysicae 16 (1998), S. 921-930 
    Details
    ISSN: 0992-7689
    Keywords: Interplanetary physics ; Energetic particles ; Solar physics, astrophysics and astronomy ; Flares and mass ejections
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We consider the prolonged injection of the high-energy (〉 10 MeV) protons during the three successive events observed by GOES in October 1989. We apply a solar-rotation-stereoscopy approach to study the injection of the accelerated particles from the CME-driven interplanetary shock waves in order to find out how the effectiveness of the particle acceleration and/or escape depends on the angular distance from the shock axis. We use an empirical model for the proton injection at the shock and a standard model of the interplanetary transport. The model can reproduce rather well the observed intensity-time profiles of the October 1989 events. The deduced proton injection rate is highest at the nose of the shock; the injection spectrum is always harder near the Sun. The results seem to be consistent with the scheme that the CME-driven interplanetary shock waves accelerate a seed particle population of coronal origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0921-0
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  • 2
    Electronic Resource
    Electronic Resource
    Neutron monitor data on the 15 June 1991 flare: Neutrons as a test for proton acceleration scenario (1995)
    Springer
    Solar physics 158 (1995), S. 395-398 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Response of Alma-Ata neutron monitor for solar neutrons from the 15 June 1991 was studied. We considered this response as a test for various scenarios of proton acceleration during the flare. The analysis of neutron monitor is an evidence in favour of the assumption of two acts of proton acceleration at impulsive and post-impulsive phases of the flare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00795674
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  • 3
    Electronic Resource
    Electronic Resource
    Implications of Proton Anisotropy Development Observed by the Erne Instrument During the 9 July 1996 Solar Particle Event (1997)
    Springer
    Solar physics 175 (1997), S. 785-795 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analysed the solar particle event following the 9 July 1996 solar flare. High-energy protons were detected by the ERNE instrument on board SOHO. Anisotropy of arriving protons revealed very peculiar non-monotonic development. A short period of almost isotropic distribution was imbedded into the prolonged period of beam-like distribution of 14–17 MeV protons. This implies the existence of a narrow magnetic channel with a much smaller mean free path than in the surrounding quiet solar wind plasma. We used Monte Carlo simulations of interplanetary transport to fit the observed anisotropies and intensity–time profiles. Proton injection and transport parameters are estimated. The injection scenario is found to be very close to the scenario of the 24 May 1990 event, but the intensity and the interplanetary transport parameters are different. The extreme anisotropy observed implies prolonged injection of high-energy protons at the Sun and at the interplanetary shock front, and either a very large mean free path (≥ 5 AU) outside the slow transport channel, or alternatively, a somewhat smaller mean free path (≈2 AU) and enhanced focusing between the Sun and the Earth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004996306331
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  • 4
    Electronic Resource
    Electronic Resource
    The 1991 March 22 flare: Possible anisotropy of high-energy neutral emission (1995)
    Springer
    Solar physics 158 (1995), S. 95-114 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We made a parameter fit to the Haleakala neutron monitor counting rate during the 1991 March 22 solar flare (Pyle and Simpson, 1991) using the time profiles of γ-rays at 0.42–80 MeV obtained with the GRANAT satellite (Vilmeret al., 1994) and the microwave data from Owens Valley Radio Observatory. We use a two-component neutron injection function to find that either an impulsive injection or the ‘impulsive-plus-prolonged’ neutron injection is possible. In both cases, the number of 〉 300 MeV neutrons emitted towards the Earth is estimated as ≈ 2 × 1027 sr−1, which is less than that of the 1990 May 24 flare by an order of magnitude. We tested if such a big difference in neutron number detected on the Earth can be accounted for solely by their different positions on the solar disk. For the estimation of the degree of anisotropy of high-energy secondary emission, we made use of macroscopic parameters of the flare active region, in particular, the vector magnetogram data from the Big Bear Solar Observatory. In our result, the anisotropy factor for the neutral emissions of the 1991 March 22 flare is only ≈ 1 – 10, which is rather small compared with previous theoretical predictions for a disk flare. Such a moderate anisotropy is due to the relatively large inclination angles of the magnetic fields at the footpoints of the flaring loop where accelerated particles are trapped. We thus concluded that the smaller number of neutrons of the 1991 March 22 flare would be not only due to its location on the disk, but also due to fewer protons accelerated during this event as compared with the 1990 May 24 limb event. For a more precise determination of the anisotropy factor in a flare, we need a detailed spectrum of electron bremsstrahlung in 0.1 – 10 MeV and the fluence of γ-ray emission from the π0-decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00680837
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  • 5
    Electronic Resource
    Electronic Resource
    The 1990 May 24 solar cosmic-ray event (1996)
    Springer
    Solar physics 166 (1996), S. 135-158 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents an integrated analysis of GOES 6, 7 and neutron monitor observations of solar cosmic-ray event following the 1990 May 24 solar flare. We have used a model which includes particle injection at the Sun and at the interplanetary shock front and particle propagation through the interplanetary medium. The model does not attempt to simulate the physical processes of coronal transport and shock acceleration, therefore the injections at the Sun and at the shock are represented by source functions in the particle transport equation. By fitting anisotropy and angle-average intensity profiles of high-energy (〉30 MeV) protons as derived from the model to the ones observed by neutron monitors and at GOES 6 and 7, we have determined the parameters of particle transport, the injection rate and spectrum at the source. We have made a direct fit of uncorrected GOES data with both primary and secondary proton channels taken into account. The 1990 May 24–26 energetic proton event had a double-peaked temporal structure at energies ∼ 100 MeV. The Moreton (shock) wave nearby the ‘flare core’ was seen clearly before the first injection of accelerated particles into the interplanetary medium. Some (correlated with this shock) acceleration mechanism which operates in the solar corona at a height up to one solar radius is regarded as a source of the first (prompt) increase in GOES and neutron monitor counting rates. The proton injection spectrum during this increase is found to be hard (spectral index γ ≈ 1.6) at lower energies (∼ 30 MeV) with a rapid steepening above 300 MeV. Large values of the mean free path (λ ≈ 1.8 AU for 1 GV protons in the vicinity of the Earth) led to a high anisotropy of arriving protons. The second (delayed) proton increase was presumably produced by acceleration/injection of particles by an interplanetary shock wave at height of ≈ 10 solar radii. Our analysis of the 1990 May 24–26 event is in favour of the general idea that a number of components of energetic particles may be produced while the flare process develops towards larger spatial/temporal scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179359
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  • 6
    Electronic Resource
    Electronic Resource
    A joint analysis of high-energy neutrons and neutron-decay protons from a flare (1996)
    Springer
    Solar physics 169 (1996), S. 181-207 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A joint analysis of neutron monitor and GOES data is performed to study the production of high-energy neutrons at the Sun. The main objects of the research are the spectrum of 〉50 MeV neutrons and a possible spectrum of primary (interacting) protons which produced those neutrons during the major 1990 May 24 solar flare. Different possible scenarios of the neutron production are presented. The high magnitude of the 1990 May 24 neutron event provided an opportunity to detect neutron decay protons of higher energies than ever before. We compare predictions of the proposed models of neutron production with the observations of protons on board GOES 6 and 7. It is shown that the ‘precursor’ in high-energy GOES channels observed during 20:55–21:09 UT can be naturally explained as originating from decay of neutrons in the interplanetary medium. The ratio of counting rates observed in different GOES channels can ensure the selection of the model parameters. The set of experimental data can be explained in the framework of a scenario which assumes the existence of two components of interacting protons in the flare. A hard spectrum component (the first component) generates neutrons during a short time while the interaction of the second (soft spectrum) component lasts longer. Alternative scenarios are found to be of lesser likelihood. The intensity-time profile of neutron - decay protons as predicted in the framework of the two-component exponential model of neutron production (Kocharov et al., 1994a) is in an agreement with the proton profiles observed on board GOES. We compare the deduced characteristics of interacting high-energy protons with the characteristics of protons escaping into the interplanetary medium. It is shown that, in the 100–1000 MeV range, the spectrum of the second component of interacting protons was close to the spectrum of the prompt component of interplanetary protons. However, it is most likely that, at ∼300 MeV, the interacting proton spectrum was slightly softer than the spectrum of interplanetary protons. An analysis of gamma-ray emission is required to deduce the spectrum of interacting protons below 100 MeV and above 1 GeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153840
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  • 7
    Electronic Resource
    Electronic Resource
    Propagation of solar cosmic rays: Diffusion versus focused diffusion (1996)
    Springer
    Solar physics 165 (1996), S. 205-208 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (‘focusing-free’) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is ‘renormalized’ by the focusing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149100
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  • 8
    Electronic Resource
    Electronic Resource
    First Energetic Particle Events Observed by the ERNE Instrument (1997)
    Springer
    Solar physics 170 (1997), S. 179-191 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The energetic particle instrument ERNE on-board SOHO started its observations on December 15, 1995. The low-energy sensor of ERNE, LED, is capable of measuring particles in the energy range from 1 to 10 MeV nucl-1. From the beginning of the year 1996 until May 22, 1996, LED-observations included four energetic particle events above threshold intensities. An energetic particle event caused by a corotating interaction region that accelerated protons upto ∽ 10 MeV, was observed during January 20–25. Another similar particle event occured on May 6–12. The events were separated by four solar rotation periods. They had similar time profiles, but the one in May had a harder spectrum and a lower intensity level. The 4He-to-proton ratios were in accordance with the solar wind value. Energetic particles observed during April 22–23 and May 14–17 were accelerated at the Sun. The first one was apparently an outcome from an active region observed on the west limb by telescopes on-board SOHO. Protons were detected at energies from 1 to ∽10 MeV. For this event, the4He-to-proton ratio in the range 1.5–5 MeV nucl-1 was ∽ 3%. No 3He ions were detected. The period of May 14–15 was, in contrast, extremely 3He-rich: it had a3He-to-proton ratio of 1.5 ± 0.6 and a 3He-to- 4He ratio as high as ∽ 8. The period of May 14–17 comprised at least three individual, one-day-long events. The first two events were 3He-rich, while the last one seemed to have a normal composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004963118224
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  • 9
    Electronic Resource
    Electronic Resource
    Impact of Magnetic Environment on the Generation of High-Energy Neutrons at the Sun (1997)
    Springer
    Solar physics 172 (1997), S. 271-278 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper demonstrates the important interplanetary manifestation of strongly tilted magnetic fields at the flare site. We start with analysis of Big Bear Solar Observatory (BBSO) observations of magnetic structures at sites of two flares responsible for 〉100 MeV neutron events. Based on these observations, a model of neutron production is considered. This model takes into account the observed large tilt of magnetic field lines at footpoints of flare magnetic loops. Results of the new calculations are compared with both previous calculations and observations. The tilt of magnetic field lines at the flare site is proved to be the most important parameter limiting anisotropy of high-energy secondary emission in solar flares.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004986526577
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